Process for electrowinning of copper values from solid particles in a sulfuric acid electrolyte

ABSTRACT

A process for electrowinning of copper values from cement copper and/or copper sulfide concentrates in which the copper bearing material is agitated in a cell in the presence of H2SO4 while temperatures are maintained above 60*C, current densities are above 60 amperes per square foot of cathode but below that current density at which electrolyte boils and deposited copper plate becomes brittle. The process is characterized by the fact that a concentration of soluble iron, in the range from 10 to 40 grams/liter, is kept in solution in the electrolyte at all times. The iron ranges from 20-40 gpl in the case of cement copper, and from 10-35 gpl in the case of copper sulfide concentrates. The soluble iron content is maintained high enough to provide a reservoir of ferric ions to aid in oxidizing and/or leaching of the copper. Current densities must be high enough to effect electrolysis with the reduction of copper and liberation of hydrogen gas in quantity to prevent attack of the cathode by ferric iron.

United States Patent [191 Wojcik et al.

[ PROCESS FOR ELECTROWINNING OF COPPER VALUES FROM SOLID PARTICLES IN A SULFURIC ACID ELECTROLYTE [75] lnventorsi Charles William Wojcik; Bruce Charles Wojcik, both of Twin Falls,

Idaho [73] Assignees: Reed Goold; Charles W. Wojcik; Gerald D. Cooper; Wilfred H.

Herrett, a part interest to each [22] Filed: July 24,1973

[21] Appl. No.: 382,145

52 u.s.c|..1 ..204/10s Primary ExaminerR. L. Andrews-- Attor'ney, Agent, or Firm-Robert R. Finch [451 Dec. 10, 1974 [57] ABSTRACT A process for electrowinning of copper values from cement copper and/or copper Sulfide concentrates in which the copper bearing material is agitated in a cell in the presence of H 80 while temperatures are maintained above 60C, current densities are above 60 amperes per square foot of cathode but below that cur- I rent density at which electrolyte boils and deposited v copper plate becomes brittle. The process is characterized by the fact that a concentration of soluble iron, in the range from 10 to 40 grams/liter, is kept in solu tion in the electrolyte at all times. The iron ranges from 20-40 gpl in the case of cement copper, and from 10-35 gpl in the case ofcopper sulfide concentrates. The soluble iron content is maintained'high enough to provide a reservoir of ferric ions to aid in oxidizing and/or leaching of the copper. Current densities' must be high enough to efi'ect electrolysis with the reduction of copper and liberation of hydrogen gas in quantity to prevent attack of the cathode by ferric iron.

I 8 Claims, No Drawings PROCESS FOR ELECTROWINNING OF COPPER VALUES FROM SOLID PARTICLES IN A SULFURIC ACID ELECTROLYTE BACKGROUND OF THE INVENTION ence of electric current, migrate to an electrode of opposite polarity. In the case of metal ions, such as copper, the metal deposits on the cathode whence it is recovered.

The usual electrolytic system for electrowinning of copper starts with a clear solution of CuSO, which has been formed in conventional manner such as by reaction between H 50 and copper oxide. Some workers have proposed direct electrowinning by treating a slurry of crushed copper oxide ores in the cell itself thus avoiding the cost and expense of leaching, filtration and purification as needed to produce a clear electrolyte. Some recently proposed'electrowinning processes have, under carefully controlled conditions of agitation, temperature and current, proven successful in the electrowinning of pure copper directly from slurries of crushed oxide ores, but cement copper and copper sulfides are not amenableto treatment in accordance with these proposals.

In electrolytic processes as heretofore practiced, -it

lyte composition, to effect direct winning of pure cop per from a slurry of cement or sulfide copper concentrates.

has been desirable to keep the dissolved iron content of the electrolyte below 2 gpl to avoid sharp drops in current efficiency; and in any event, the iron content was kept below 9 gplin order to protect the cathode and any deposited copper from attack by ferric iron which attack'defeats the recovery of copper.

SUMMARY or THE INVENTION It is the primary object of this invention to provide a process for the direct electrowinning of-copper from v slurries of solid cement copper or copper sulfide concentrates in an H 50, electrolyte.

It is another object to provide an electrowinning process for direct recovery of high purity copperfrom cement copper and copper sulfide concentrates at high current densities and efficiencies; and under conditions such that the cathode is protected from ferric iron at tack without generation of H 8 or excess H 80 Another-object isthe provision of an electrowinning process in which-the capital cost'and expense of operation is reduced by elimination of the equipment re-- ble iron, under carefully selected and controlled operating conditions-of temperature, current and electro- In brief, the process invention contemplates the violent mixing of finely divided cement copper or sulfide copper concentrates with a sulfuric acidcopper sulfate solution in which is maintained a significant concentration of dissolved iron while subjecting the mixture to a current field in an electrolytic cell.

In the case of cement copper, the electrolyte is usually saturated at about 35-40 gpl iron and the iron concentration is desirably maintained in a range of 20-40 gpl.

Although the exact function of the dissolved iron is not known, it is theorized that the high current density employed in this invention oxidizes ferrous to ferric which then acts to oxidize or ionize elemental cement copperwhich, after going into solution, is in turn reduced by electrolysis to elemental copper that is deposited at the cathode. The iron must be present in a sufficient concentration to oxidize the copper and also to provide a reservoir of ferrous iron to be simultaneously oxidized to ferric iron at the anode so that the process may operate continuously withferric ironin solution being consumed in oxidation of copper while ionized copper is reduced and plated at the cathode at the same rate that ferrous iron is oxidized at the anode.

Assuming the reaction is as described, then the cementcopper goes into solution by leaching in accordance with the equation:

but this proceeds at a practical rate only when the voltage and current densities as well as H and CuSO concentrations are sufficiently high.

According to our studies, in the case of cement copper the reaction proceeds at a practical rate when the dissolved iron concentration is 20-40 gpl, the H SO starting concentration is 200-240 gpl, the solution temperature is above C, the DC voltage is from 2- 5 volts (measured between the anode and cathode) the current density is above 60 amp/ft but below that which causes boiling of electrolyte and/or formation of brittle plate, the latter being determined emperically. (The top limit we have so far observed is about 300 amplft In order that the reaction proceed properly, it is also necessary that the slurry of cement copper in electrolyte be agitated violently. Also, the dissolved copper concentration of the electrolyte should be maintained in the range of 2040 gpl. Below 20 gpl .Cu, a brittle and/or powdery plate will be formed. The upper limit is unimportant. This concentration is conveniently obtained at the outset by the addition of copper sulfate, although it will build up by itself as power is supplied to the cell.

' The presence of at least '10 gpl of dissolved iron is adding ferric sulfate. The addition of a soluble copper salt (CuSO at the outset is also desirable although, as noted, if iron is present, thecopper concentration will be built up and then maintained at a selected level.

In the case of sulfide-concentrates, the specific operating conditions may vary from those required from cement copper, however, the basic requirements of dissolved iron and high current densities remain.

In the case of Cu S a basic reaction is apparently CugS 2Fe CuS 2Fe Cu withthe Cu thereafter being reduced to plate at the cathode while ferrous iron is reoxidized at the anode.

CuS is only difficultly soluble in the acid electrolyte yet under the conditions of my process the ore is depleted relatively easily which means that some mechanism operates to dissolve or leach the copper. My work shows that the rate of copper recovery varies directly with the iron content of the electrolyte. Thus, it is believed that the iron does enter into or perhaps catalyzes rapid dissolving of the copper.

in general, for sulfide concentrates during operation the electrolyte should contain -25 gpl dissolved iron and at.least 25 gpl dissolved copper. The electrolyte temperature should be above 60C but below the boiling point of the solution. Voltage should be above about 2.5 volts. Current densities should be above 60 amp/ft cathode area up to a maximum where brittle plate or boiling of electrolyte occurs. In general, high current densities result in higher recovery rates.

It is important that the slurry be violently agitated in the cell during the process. This accomplishes several things. It insures maximum contact between the solids and electrolyte, avoids uncontrolled polarization at the electrodes, insures contact between liberated hydrogen gas and ferric iron adjacent the cathode to protect the cathode and the deposited copper from attack by ferric iron. Also, if the agitation is carried out by' movement of the cathode, the plate quality will be further enhanced by the movingcathode target.

Extensive tests were performed on cement copper and chalcocite concentrates from several sources.

The equipment used comprised a octagonal shaped tank with its wall serving as the anode. An oscillating cathode was mounted in the tank. The cathode was formed with several removable stainless steel plates 'which permitted variation in the cathode area to provide a wide variation of current densities with a given power source Paddles were mounted on the cathode structure to agitate the slurry as the cathode reciprocated. Power was supplied by a conventional full wave rectifier DC power supply. The cell tank was built to contain about inches slurry and the cathodes were arranged to be immersed to a maximum depth of about 18 inches. Each cathode plate thus had an effective single side surface area of about 0.3l ft In the test arrangements both sides were plated. Thus, each plate had a total effective area of 0.62 ft.

The cellwas filled and emptied manually. Additional copper-bearing materials were added and samples taken as desired during operating. For final analysis of the tails. the tank was emptied entirely. All tests and assays were performed in accordance with accepted techniques.

ln examples. the acid content of the electrolyte is recited at the start of a test and is based on the known materials used in making up the solution. The acid requirements are simply that only enough acid is required to keep the reaction going at an acceptable rate. Too much acid will slow down reaction rates. The current density affects the acid concentration. Too low a density will cause undesirable acid build-up in the system with reduction in recovery rates. Increasing current will stop or even reverse acid build-up. Thus, the current Test Dissolved Dissolved Voltage Current Temp No. iron Content Cu gpl Density gpl Amps/ft l 1.6 l0.6 2.8 44.4 43 2 l3.l 19.7 3.0 55.5 55 3 13.4 23.6 3.4 55.5 40 4 l3.4 23.5 3.4 66.6 52 5 l3.8 23.9 3.0' 44.4 5! 6 25.4 24.4 3 7 66.6 54

In the foregoing tests copper deposited at the cath ode, in the time indicated. was:

Test 1: After 45 minutes, only unacceptable powder deposited;

Test 2: After 60 minutes brittle plates were formedtotal copper recovered was 399 grams. Power consumption was 0.853 KWH/lb copper recovered;

Test 3: After 60 minutes a plate of improved appear ance. but still somewhat brittle was harvested-total weight of copper recovered was 358.4 grams, power consumption was 1.09 KWH/lb copper recovered;

Test 4: After 60 minutes bright flexible plates were harvested. Total weight of copper recovered was 479 grams, power consumption was 0.967 KWH/lb copper recovered; Test 5: After 60 minutes dense bright flexible plates were harvested. Total weight of copper recovered was 304 grams, power con sumption was 0.925 KWH/l-b copper recovered;

Test 6'. After 60 minutes, dense bright flexible plates formed. Total weight of copper recovered 407 grams, power consumption was 1.24 KWH/lb copper recovered.

The tests demonstrate that the ability of the system to dissolve and plate copper varies directly with the dissolved iron content and. further, that the quality of deposited plate increases as the dissolved iron content increases. The plate quality is enhanced by the ability of the H to reduce corrosive ferric iron adjacent the cathode and by the constant availability of ferric ions elsewhere in the system to oxidize elemental copper into solution.

Other operating tests were performed in the same test equipment on various cement copper and chalcocite concentrate samples. All tests were conducted with vigorous agitation. All currents are DC.

EXAMPLE f A wet chalcocite concentrate containing 37.2 per cent copper by weight (as Cu S) and ground to pass a 325 mesh screen (Tyler) was mixed in the tank with 45 liters of an electrolyte initially containing in solution 100 gpl H 50 l5 gpl ferric iron and 30 gpl of copper. Voltage averaged 3.5 and a steady current density of EXAMPLE n The same setup used in Example 1 was employed, but an additional 2419 grams of concentrate was added and the system operated at an average of 3.6 volts and a steady current density .of 74 ampslft for 4 hours.

Temperature was steady at about 61C. After four EXAMPLE 111 An 1880 -gram sample of wet chalcocite containing about 46.8 percent copper as Cu S and ground to pass a 200 mesh screen (Tyler) was mixed in 44 liters of an electrolyte containing 200 gpl H 50 27.4 gpl dissolved'iron and 39.3 gpl dissolved copper. The system was run for 4% hours during which the voltage varied from 3.9 voltsdurin'g the first hour to 3.35 volts during the last hour. Current density was a constant 66.6 amps/ft? Temperature ranged from 47-64C.

At the end of the test, the electrolyte still contained 32.7 gpl copper as compared to the start of 39.3 gpl. The weight of copper recovered at the cathode was 1179 grams. Of this, 291 grams was taken from the electrolyte while the balance was recovered from the concentrate. lgnoring experimental error, the recovery was essentially 100 percent.

The following tests were carried out in a smallercell than the other tests. It was essentially of the same design, but shallower and with a smaller cathode area..

EXAMPLE IV A 1691 gram sample of wet cement copper, containing about 47.9 percent copper was mixed with 27 liters of electrolyte containing 200 gpl H 80 30 gpl dissolvedferric iron and 30 gpl dissolved copper. The system was operated for a total of four hours. Additional amounts of cement copper, totalling 3182 grams, were added at about 16 hour intervals. Thus, the cumulative total wet cement copper processed in the cell was 4873 grams containing 2335 grams of copper. Voltage ranged from a high'of 4.9'to a low 3.7. Current density at the cathode also variedfrom a high of 250 amps/ft to a low of 150 amps/ft? These values are shown in Table A.

TABLE A-Continued Time Voltage Total Current Temp Amperage Density C.

. Amps/ft (changeover in current made at this time) Samples of copper plate were taken from one cathode plate at 2 hours (47.6'grams) and from the same cathode plate at 3 hours (57.5 grams). At the end of the test, all cathode plates were stripped, the product sheets weighed and compared with the product sheets taken during the test. A total of 2150 grams of copper was recovered at the cathode. All plates were of high quality, dense and flexible. At the finish, the electrolyte contained 40.4 gpl ferrous iron and 40.7 gpl copper. All of the 2150 grams of plate copper plus the 288 grams increase in dissolved copper content of the electrolyte during the test was extracted from the cement copper solids. On the basis of the weight of copper recovered from the cathode the percent recovery is about 92 percent and if one considers the additional copper in solution as being effectively recovered, and allowing for experimental error, the recovery is at percent.

' EXAMPLE V A 1480 gram sample of wet chalcocite concentrate containing 38.7% (573 grams) copper ground to pass a 325 Tyler mesh screen was'mixed with 27 liters of electrolyte initially containing 100 gpl H 50 30 gpl copper and 30 gpl iron as ferric sulfate. The test was conducted for a total of six hours. Additional amounts of concentrate containing another 2074 grams copper were added in increments during the test. Thus, a total of 2647 grams copper as sulfide was processed. Voltage ranged from a high of 5.2 to a low of 4.2 volts. Current density at the cathode was at amp/ft during the first hour and 200 amp/ft during the balance of the test. Temperature started at 60C and climbed to 79C for the last 3 hours. A total of 2645 grams of copper was recovered at the cathode while the electrolyte showed a loss of 10 grams copper. Thus, 2635 grams of copper was recovered from the concentrate. This represents a recovery of 99.55 percent from the processed TABLE B Elapsed Copper lro'n Ampft Voltage Time-hrs gpl gpl cathode DC 0a....) 30. 30.* 150 4.9 1 39.8 25.1 150 4.4 1** 39.8 25.1 200 4.4 2 39.8 28.1 200 5.2 3 37.4 29.9 200 5.0 3 3 4.4

TABLE B-Continued Elapsed Copper Iron Ampft Voltage Time-hrs gpl gpl cathode DC At start iron was as ferric. At all other times values are for ferrous.

"Amperage was increased at end of one hour 500 ml H 80 addcdat end of three hours. (in ail work 60 Baume acid was used).

On visual inspection the cathode product was of high quality.

Many other tests were made in the same equipment on cement coppers and chalcocite concentrates from various sources. The operating conditions were within the limits set forth in the foregoing examples and gen- I eral text. In all cases, it was possible to produce a good plate when the dissolved iron content of the electrolyte and current densities were in the stated ranges.

Due to the cost, only part of the copper product was subjected to laboratory assay for purity. However, the copper produced in two additional runs made in accordance with this invention was assayed. One run was made on an Anaconda cement copper containing about 85 percent copper (dry basis), the resulting plate formally assayed at 99.9965 percent copper. Another run was made on a chalcocite concentrate containing only 26.4 percent copper. The resulting plate formally assayed at 99.9942 percent copper. This is remarkable purity and clearly demonstrates the ability of the process to produce high grade copper directly from heretofore difficulty treatable materials. I

Although actual tests are reported only on cement copper and chalcocite sulfides, it is obvious that the process will apply to any copper-bearing sulfide concentrates.

As used herein, cement copper refers to that finely divided copperformed in well known manner by dumping of copper solutions on steel whereby the copper r'eplaces the iron and is recovered.

Copper bearing sulfides amenable to processing in accordance with my process include the common naturally occurring ores, or concentrates thereof, such as bornite (Cu FeS chalcocite (Cu S) chalcopyrite (CuFeS and covellite (CuS). Also, actual tests were conducted on Chrysocolla (CuSiO '2l-l O), under the conditions outlined for sulfides; and it reacted similarly to the chalcocite concentrate. yielding a high quality copper.

it operates without undesirable release from the cell of gases. such 0 H or H 5 and the like.

We claim:

1. A process for electrowinning of copper values from a finely divided copper-bearing solid selected from the class consisting of cement copper and copper sulfides comprising the steps of establishing a source of copper for leaching by continuously agitating a quantity of said copper-bearing solids in an H electrolyte contained in an electrolytic cell having a cathode and an anode, establishing and maintaining in said electrolyte a dissolved iron concentration of at least ten grams per liter and leaching copper from said source while depositing copper on said cathode by continuously passing a direct current of at least two volts through said electrolyte between said cathode and anode at a current density in excess of about 60 amperes per square foot of cathode area whereby to effect deposition of copper on said cathode concomittently with liberation of hydrogen thereat.

2. The process according to claim 1 in which a dis solved copper concentration of at least 20 grams per liter is maintained in the electrolyte.

3. The process according to claim 1 in which said direct current has a voltage in the range from 2 volts to 5 volts.

4. The process according to claim 1 in which iron concentration of the electrolyte is established by the addition thereto of ferric sulfate.

5. The process according to claim 1 in which said copper-bearing solid comprises cement copper, and the iron content of said electrolyte is established in a range from 20-40 grams per liter by the addition thereto of ferric sulfate.

6. The process according to claim 5 in which the H 80 content of said electrolyte is adjusted by increas ing current density to decrease l-I SO content and by decreasing current density to increase H SO content.

7. The process according to claim 1 in which said copper bearing solid comprises a material inwhich the copper occurs as Cu S, and the iron content of said electrolyte is established in the range of from 10 to 35 grams per liter.

8. The process according to claim 7 in which the l-l SO content of said electrolyte is adjusted by increas ing the density of said direct current to decrease H 50 and decreasing said density to increase said H 50 

1. A PROCESS FOR ELECTROWINNING OF COPPER VALUES FROM A FINELY DIVIDED COPPER-BEARING SOLID SELECTED FROM THE CLASS CONSISTING OF CEMENT COPPER AND COPPER SULFIDES COMPRISING THE STEPS OF ESTABLISHING A SOURCE O COPPER FOR LEACHING BY CONTINUOUSLY AGITATING A QUANTITY OF SAID COPPER-BEARING SOLIDS IN AN H2SO4 ELECTRLYTE CONTAINED IN AN ELECTRLYTIC CELL HAVING A CATHODE AND AN ANODE, ESTABLISHING AND MAINTAINING IN SAID ELECTRLYTE A DISSOLVED IRON CONCENTRATION OF AT LEAST TEN GRAMS PER LITER AND LEACHING COPPER FROM SAID SOURCE WHILE DEPOSITING COPPER ON SAID CATHODE BY CONTINUOSLY PASSING A DIRECT CURRENT OF AT LEAST TWO VOLTS THROUGH SAID ELECTRLYTE BETWEEN SAID CATHODE AND ANODE AT A CURRENT DENSITY IN EXCESS OF ABOUT 60 AMPERES PER SQUARE FOOT OF CATHODE AREA WHEREBY TO EFFECT DEPOSITION OF COPPER ON SAID CATHODE CONCOMITTENTLY WITH LIBERATION OF HYDROGEN THEREAT.
 2. The process according to claim 1 in which a dissolved copper concentration of at least 20 grams per liter is maintained in the electrolyte.
 3. The process according to claim 1 in which said direct current has a voltage in the range from 2 volts to 5 volts.
 4. The process according to claim 1 in which iron concentration of the electrolyte is established by the addition thereto of ferric sulfate.
 5. The process according to claim 1 in which said copper-bearing solid comprises cement copper, and the iron content of said electrolyte is established in a range from 20-40 grams per liter by the addition thereto of ferric sulfate.
 6. The process according to claim 5 in which the H2SO4 content of said electrolyte is adjusted by increasing current density to decrease H2SO4 content and by decreasing current density to increase H2SO4 content.
 7. The process according to claim 1 in which said copper bearing solid comprises a material in which the copper occurs as Cu2S, and the iron content of said electrolyte is established in the range of from 10 to 35 grams per liter.
 8. The process according to claim 7 in which the H2SO4 content of said electrolyte is adjusted by increasing the density of said direct current to decrease H2SO4 and decreasing said density to increase said H2SO4. 